1. Field of the Invention
The present invention relates to a marine vessel including a lift force difference generating unit which generates a lift force difference between a port side and a starboard side of the marine vessel, and a marine vessel running controlling apparatus for a marine vessel.
2. Description of the Related Art
An inertial navigation system provided in a marine vessel is generally capable of detecting the yaw angular speed, the roll angle, and the pitch angle of the marine vessel. In an ordinary marine vessel running state, the roll angle of the marine vessel is zero during straight traveling of the marine vessel, and is non-zero during turning of the marine vessel. On the other hand, the marine vessel steadily has a non-zero roll angle over a long period of time when traveling with its gravity center shifted to a starboard side or a port side due to unevenly loaded cargo or due to wind blowing on its broadside. Such a steady-state roll angle, i.e., an average of roll angles measured over a long period of time, is herein referred to as “heel angle”, which is intended to be differentiated from the roll angle. The attitude of the marine vessel observed when the heel angle is zero with respect to a water surface or a transverse axis of the marine vessel is parallel to the water surface is herein referred to as “neutral attitude”.
When a marine vessel 80 travels in a non-neutral attitude at a non-zero heel angle as shown in FIG. 11A, a lift force difference occurs between a starboard side and a port side of a hull 81 of the marine vessel 80, making it difficult for the marine vessel to travel straight. At this time, as shown in FIG. 11B, an operator of the marine vessel operates a steering wheel 82 to balance the lift forces on the starboard side and the port side, thereby causing the marine vessel to travel straight. In this state, however, the traveling direction of the marine vessel 80 does not coincide with the bow direction of the marine vessel 80, so that the hull 81 is subjected to a great resistance. This reduces the propulsive efficiency of a propulsion system 83.
Automatic attitude controlling apparatuses for controlling the marine vessel in the neutral attitude are disclosed, for example, in U.S. Pat. No. 5,474,012 and Japanese Unexamined Patent Publications No. HEI9(1997)-76992, No. HEI9(1997)-315384, and No. 2004-224103. With the use of any of these apparatuses, the trim angles of outboard motors or the angles of flaps are controlled according to an output of a roll angle sensor to keep the heel angle at zero.
If the operator performs a steering operation to nullify the heel angle, however, the automatic attitude controlling apparatus is no longer operative. Therefore, the marine vessel continuously travels with its propulsion system driven at a reduced propulsive efficiency.